Candles and incense have the power to evoke memories. See the flickering flame and you may recall romance, relaxation, or religious rituals. Depending on the scent, catching a whiff of some wafting fragrance can send you back in time – to your childhood church, to your grandma's kitchen. Let's stop to consider 8 things to know about the candles and incense that burn through so many parts of our lives.

They offer us a chance to pray, praise, or celebrate. Many of us blow out candles on birthday cakes to mark each year we've been alive. Many religious ceremonies and cultural traditions also center on the candle and its flame: the Hanukkah traditions of Judaism, the symbolic lit pillars of Kwanzaa in the African-American community, the festive flames of the Hindu and Sikh festival of Diwali, the votives and altar prayers for lost loved ones in the Catholic Church, and the incense burnt at Buddhist shrines.

Candles and incense can calm, soothe, or create a mood. Practitioners of meditation often look into a candle's flame to steady their gaze or burn incense, the scent a focal point for their attention. Those seeking simple serenity may light candles or burn incense in their home, while the soft warmth of candlelight can set the mood for romance.

While they may set a mood, candles can also pose a fire hazard. Obviously, right? But have you ever seen a film or soap opera in which someone lights what seems like hundreds of candles all over their bedroom? You have to wonder how easy it is to relax or "get in the mood" when you’re surrounded by so many tiny flames! To be safe, keep candles far from materials that may catch fire, such as paper, curtains, clothing, and linens. Do not leave candles burning when no one is in the room, and always blow out flames before falling asleep. Also, do not leave lit candles anywhere that children or pets can reach them. To control the size of the flame, keep the wick trimmed short. Always trim the wick to a height of 5–7 mm before lighting and trim it again after a couple of hours.

You have to be tricky with that wick. When choosing a candle, you might not think much about the wick, but those little nubs are a big deal! Wicks with metal at their core may contain lead. Long-term use of these types of candles can contaminate the surroundings and expose you and your family to lead. Be sure to select candles that have a wick made from braided or twisted plant fibre, containing no metal. You can test the wicks of candles you already own: Remove the wax from the tip of the wick and pull apart the strands of fibre to see if there is a metallic core. Rub this core on a piece of white paper. A gray mark left behind indicates lead.

Candles and incense can affect air quality. As candles or incense burn, tiny particles smolder and flake off into the air. When this soot is inhaled, it can get into the airways and lungs, possibly causing irritation. This can worsen asthma symptoms. You may come across candles labelled as "soot-free," but there is no such thing as a soot-free candle. Burning something will always cause soot. Certain types of candle – beeswax and soy, for example – may create less soot than wax or paraffin candles.

Candles and incense may worsen symptoms in allergy sufferers. Most of us know the twitchy feeling our noses get when we smell strong fragrances, like floral-scented candles or pungent incense. For some sensitive-nosed folks like those who have allergies, the odours of candles and incense may trigger runny nose and watery eyes. If this happens to you, you may be able to pinpoint which scents set you off. You may be fine with frankincense but sneeze at cinnamon.

Incense use has been linked to cancer risk. Researchers in Taiwan wondered about the air quality of the city's temples – air filled with soot and smoke from burnt incense. They collected air samples from inside a temple and found a very high concentration of polycyclic aromatic hydrocarbons (PAHs), cancer-causing chemicals released by burning certain substances. Levels of PAH were up to 45 times as high as in homes where people smoke tobacco. Other studies linked long-term use of incense to an increased risk of respiratory cancers. For casual incense users, moderation and proper ventilation are recommended.

Candles should stay far from your ear! "What's that?" you say. Ear candling is a practice in which a hollow, cone-shaped candle is used to extract wax from the ear. It's believed that the flame's heat somehow vacuums earwax right out of the ear canal. But this alternative therapy has been disproved and is, in fact, potentially dangerous. People have been burned, and hair has caught on fire. And the mucky-looking residue left behind after the procedure is wax - but it's just candle wax, not earwax. If you're looking for relief from built-up earwax, check with a doctor.